Wednesday, 4 September 2019

Solar Thermal Innovators

Are These Solar Thermal Entrepreneurs Going to Move the Dial for Solar Thermal?

At the "Setting Sights on Scottish Solar 2019" conference this week in Edinburgh,  we heard from three individuals that are hoping that their innovative ideas are going to set the solar thermal market alight again.

Since the glory days of 2010 when, according to statistics from the Solar Trade Association, the UK installed nearly 90,000 square metres of solar thermal panels the market has reduced in size every single year.  Only 7,000 square metres were installed in 2018.   In an introduction to the session, the Chair of the STA's Solar Heating Working group, Dr Richard Hall revealed that this is not simply a UK phenomenon - solar thermal is in retreat in almost all international markets.

Annual solar thermal sales in the UK according to statistics compiled by STA

Solar PV panels continue to decrease in cost and increase in power output.  Excess PV-generated electricity can be inexpensively diverted to heat hot water in your tank via its immersion heater but can also charge large batteries to provide evening electricity use, and prevent a trip to the petrol filling station by topping up your electric car.  Where is the place for solar thermal in this brave new world of smart electricity grids and electricity 'pro-sumers'?
Our three brave entrepreneurs each believe that they have found a new angle that can make a difference to the appeal of solar thermal panels.

Image: SolarisKit

Faisal Ghani of Solariskit  sidesteps the problem of declining traditional markets for solar thermal by attempting to create a completely new market for solar water heating in sub-saharan Africa and other hot countries.  His 'flat-pack' solar panel features a black slinky hose arranged in a conic spiral and contained within a clear plastic pyramidal cover.   It is intended to be low-cost and simple to install and maintain.

solarblogger says: Faisal has come up with a really striking geometry for a solar collector and it is clear that the material costs could be low, if SolarisKit can get enough volume in manufacture.  It's low-weight, flat-pack design will doubtless be helpful for supply chains across rough terrain.  However it will be up against the most cost-effective of solar thermal panels - the thermosyphon Chinese combi systems that include a panel and an outdoor cylinder at rock-bottom prices.

Image: Soltropy

By contrast, Stuart Speake from Soltropy thinks that dairy farmers with a large hot water demand are ideal customers for his solar panel, and his business appears to be the furthest along of the three in that is financed by product sales rather than investors and grant money.  Soltropy's evacuated tube solar collector is freeze tolerant.  Water heated by the evacuated tubes as it is pumped along a copper header pipe returns down a second pipe made from a flexible, compressible material that runs inside the first.  If the water in the pipe freezes, the inner compressible tube is squashed up to prevent the pressure build up that would normally cause pipes to burst in freezing weather.  A solar thermal system that does not require antifreeze has greatly reduced maintenance requirements.

solarblogger says:  I love this idea- it achieves the same goals as the old Solartwin freezable absorber, but elegantly avoids that product's serious performance compromises by removing the compliant tube from the heat transfer pathway.  There is no doubt that the breakdown of antifreeze over time is the source of many of the reliability issues of solar thermal, and that many customers simply don't do preventative maintenance on their solar heating systems.  Being able to reliably remove antifreeze from solar thermal is a big step forward, but I'm not sure that on it's own it is enough to change the fundamental attractiveness of the technology.

Image: Senergy

We also heard from Christine Boyle of Senergy, whose company has developed an all-polymer solar thermal panel.  The absorber, fluid flow channels and panel sides are extruded from specially developed material consisting of  carbon nanotube loaded polymer.  This new material has high softening temperature compared to most other plastics, improved thermal conductivity and increased strength. The latter of these properties of the material allows it to be made with thinner walls which also enhances heat transfer to the working fluid.

The extrusion is finished off with injection moulded end-caps to complete the fluid circuit and a clear polycarbonate coverglass is added on top.  There are inevitably some performance penalties compared to conventional solar collectors, the insulation is de-rated to limit the stagnation temperature and the absorber is not spectrally selective.  The energy yield will be reduced to some extent for most applications, but  Senergy claim that their panels are 50% of the price of regular solar thermal panels, which if it is borne out would represent a very significant saving.

solarblogger says: All-polymer panels have been seen as the holy grail of low-cost solar thermal by many people for some time.  Other advocates include Aventa Solar from Norway, which has developed an all-polymer absorber, but I really like the design for manufacture that Senergy has come up with.  However, I remain pretty sceptical that a lower panel cost will be a silver bullet for solar thermal.  Conventional solar thermal panels  made in vast quantities, for example by GreenOneTec  leave the factory for less than EURO 100/m2.  Consequently the manufactured cost of the panels represents less than 10% of the price of a typical domestic-scale installation, with other costs such as customer acquisition, roof access, piping, insulation and controller accounting for the rest.

So what do you think, are these three solar thermal innovators going to be the next big thing or are they trying to push water uphill in such adverse market conditions for solar thermal?

Friday, 5 April 2019

Why Choose a Career in the Solar Industry?

Why should anyone take a job in the solar industry?  It may seem like a strange time to be talking about a skills shortage just after Feed in Tariffs have closed, government is yet to set out a clear route to market for exported electricity, and in the week that Ikea pulled its domestic solar offer in the UK.

But that's what I'm hearing from colleagues.

They talk of job adverts sitting open for months on end, difficulty getting electricians to take roles in solar and people moving out of solar divisions and back into regular M&E contracting or roofing.

The challenge, I believe, is one of perception - that solar is just a fad - lots of installations while the government paid for them, but all gone today, right?

Feed in Tariffs were cut, and cut again, and have now been taken away.  Solar farms once popped up like mushrooms and then years went by without ground being broken for a new one.  Taxes have been imposed on businesses with solar panels, higher electricity standing charges are proposed for people with solar on their homes.  Solar boom then bust, and bust and some more bust is the diet that the news media has fed the public.  Little wonder colleagues across the industry are saying that attracting talent right now is proving to be a challenge.

Our industry has driven forward at a pace that has regularly sent waves of panic through those government departments tasked with supporting the transition to a green economy.  Support scheme after support scheme that looked well-designed and rational when announced were quickly overtaken  by the relentless and rapid innovation of the solar sector.  As solar costs fell, financial returns rose, deployment volumes exploded and government support schemes ran out of money.  Spain, Italy, Germany, UK - the list of countries rapidly back-tracking on support schemes goes on.

Economies of scale, automation of manufacturing, ever-higher solar panel efficiency, new financing models, reduced risk for investors - all these have driven down the cost of solar and increased the financial attractiveness of the technology.  Crucially, this happened at a speed that governments were unable to respond to.  The result was often a knee-jerk approach to policy development.

Our industry has often, by necessity, been complicit in the tone of the media coverage, publicly regretting the reckless treatment of theindustry by our government, while at the same time talking up the long-term prospects.  Inevitably, press coverage focused on the negative messages.  Faced with cliff-edges created by government flip-flopping, what would you expect a solar installation business to do, apart from tell people to 'get in quick' before they take it away?  Regrettably, the industry's own marketing has also helped create the message that solar is only a 'fad'.

No more!  The era of solar as 'subsidy-junkie' is over.  A tipping point is already here.  In more and more applications, in more and more climatic zones, solar stands without need for grants or support schemes.  Every new innovation that drives down the cost of solar energy simply expands the number of applications where it pays for itself and grows demand for solar equipment, installation and maintenance services.  As demand grows, economies of scale increase, which drive down costs again and a virtuous circle is created.

In sunny climates solar already competes with all othersources of electricity generation at wholesale prices.  In less irradiated places like the UK solar-generated electricity is cheaper than retail electricity, particularly large scale solar applied to commercial buildings or as ground arrays with an energy supply agreement with a large consumer of electricity.

For new buildings reaching for ever higher energy efficiency standards and for low energy refits of existing buildings solar is a necessary demand-reduction measure, reducing electricity consumption from the grid.

Millions of new electric vehicles will achieve similar results for the cost of batteries.  These vehicles, each with a range that far exceeds most people's daily requirements, will store electricity generatedduring the day and release it at night, enabling ever-higher quantities of solar on the electricity grid.

As well as electrifying our transport, it is now widely accepted that the heating of our buildings must also be electrified.  In a move away from carbon-emitting gas and oil - we will be using either heat pumps or direct electric heating and high levels of thermal insulation to keep our buildings warm.  Demand for electricity will increase significantly - greater efficiency of appliances and gadgets will only offset the increase in their number.

So the future for solar is bright.  Anyone considering a career move into the solar industry should consider the following points:

  1. They would be joining a growth industry with strong fundamentals, an industry that will support a long career. 
  2. Work that provides meaning and clear social benefits is more and more important to everyone, but especially younger people setting out on their careers. The solar industry offers socially rewarding work, where you feel part of the solution rather than part of the problem in the fight against global climate change. 
  3. Roles in the solar industry offer transferable skills such as project management, risk management, international supply chain development, electrical and structural design.
  4. You will become more popular at parties!  When asked 'so, what do you do?' the solarblogger can attest that saying you work in the solar industry is a real conversation-starter, in stark contrast to the conversation-killer of a previous job in 'instrumentation for genetic analysis'....

So what do you think?  Are you finding it difficult to recruit?  If so, what do you think the industry could and should do about it?

Sunday, 17 February 2019

The Smart Export Guarantee Scheme (SEG)

Why is central government continually surprised that when the big energy companies are asked to ‘do the right thing’, they instead do what is right for them?

Central government seems to love handing responsibility for delivering energy reduction targets over to the big energy suppliers.  The scheme names come and go -  CESP, CERT and ECO – but the common factor has been to require energy companies to invest in energy efficiency measures such as loft insulation, and cavity wall insulation for homes.

Pause for a moment to think about it.  You’re asking a business to do things to reduce demand for its own product – energy.   How surprised should be we be that that foot-dragging, missed targets and ineffective measures have been the result?

In 2014, many of the energy suppliers were fined for failing to meet their targets to install insulation. British Gas was fined £11million, a development which their PR department brazened-out as a charitable donation.  One is left wondering if the energy companies see these fines a small price to pay instead of helping people spend less on energy.

With the government's new proposals for a Smart Export Guarantee (SEG) are we again about the make the same mistake by asking the big energy companies to decide what the ‘market price’ for electricity exported by householders and businesses with solar panels?

Why we Need a Smart Export Guarantee

Many people in the solar industry that I speak to have pretty mixed feelings about the Feed in Tariff.  They recognize the transformative effect of 19 years of subsidy on the industry, helping it to achieve scale and cost-competitiveness with fossil energy.  At the same time, they regret the reckless way that the scheme has been managed.  Successive ministers at DECC and then BEIS have inflicted real pain on many good people who had invested their time, energy and money in solar businesses an effort to be part of the solution.

As a consequence, the industry is genuinely looking forward to a future where it no longer needs ‘help’ like that from government and the technology can stand on its own feet as a significant contributor (maybe the dominant contributor worldwide) to the clean energy revolution.

It remains crucially important for the sector that householders and businesses that invest in solar are able to sell generated solar energy that they cannot use themselves.  This makes possible efficient and cost-effective solar systems that minimize the cost of energy rather than being sized to just meet demands in the building at times of peak output.

So, as the Feed in Tariff (FIT) draws to a close on March 31st, government is consulting on a new scheme, the Smart Export Guarantee (SEG) – that requires larger energy suppliers to purchase excess solar energy from small generators at a fair market price.

There is much to welcome in the proposals for SEG
  • the Microgeneration Certification Scheme is thrown a life-line as the only way to qualify,
  • there is to be no requirement for the building to achieve a certain energy efficiency level (EPC), a requirement in FIT that excludes many older and listed properties
  • installations that occur after the FIT closes but before the SEG is available will be able to join the SEG as soon as it opens
  • export will be metered and not estimated (as in the FIT), rewarding people that install larger systems
  • a central database of solar installations will be maintained beyond the FITs
  • the high price for bought in electricity compared to the low value of exported will encourage the deployment of battery storage and electric vehicle charging (when compared with other arrangements, for example net metering)

Concerns About the Detail

However, there are two big concerns with the proposals as they currently stand:
  1. Smart metering IT systems are not up to the job at present
  2. The reliance on conflicted businesses to set a market price

Smart Metering Systems

At recent Solar Trade Association meetings we were astonished to hear that the SMETS1 smart meters that have so far been installed ‘go dumb’ as soon as you change supplier.  Although second generation SMETS2 smart meters fix this problem, the IT infrastructure that collects the data is not yet ready to a point where this data can be shared between an energy supplier and a separate company that you have signed your SEG deal with.

It would be just like government to say ‘well, we’ve done our bit’ as they launch a completely theoretical SEG scheme, which nobody can use in practice because the billing arrangements are not ready.

That’s why we need something - dare I call it a ‘backstop’ - that makes the SEG work from day one and creates an incentive for energy companies to sort out the IT, rather than having a strong incentive to drag their feet and take as long as possible to prevent the SEG ever happening.

A backstop could look a lot like the export tariff part of the current Feed in Tariff:

  • A fixed value, for example £0.04 /kWh
  • A deemed export 50% of generation 

This would create a strong incentive for the energy companies to pull out their fingers because they are likely to be over-paying for generation where they cannot meter it.

Setting  a Market Price

Electricity costs vary during the day as supply and demand varies.  The industry would be absolutely delighted if export was paid a fair market price at the time of export – that is a price set between a willing buyer and a willing seller.

The preferred option in the SEG consultation is to simply leave it to the energy suppliers to set the price, with the only control being that the price is higher than £0.00

My concern is that the proposed mechanism will not result in a fair market price, because the companies that are being relied upon have every incentive to keep the amount of solar installed as low as possible.  They are conflicted because every time a household or business installs solar it will buy less power from the energy suppliers.  Setting a higher price for exported energy would make solar a more appealing investment and harm the business models of the energy suppliers.

The energy companies do not meet the requirement of being a ‘willing buyer’ for the power and a fair market price will not result. There is a market failure and government cannot leave pricing the invisible hand of the market – except that it can, it just needs another way.

The ‘market’ already sets a price for electricity – and one that is free from the conflicts set above.  For example market exchange Nordpool publishes day ahead pricing for wholesale electricity on an hourly basis.  These prices could be better taken as the ‘market price’ for electricity between a willing buyer and a willing seller.  Energy companies should be required to purchase from microgenerators at the wholesale market price.

Wednesday, 28 November 2018

The Grand Challenge Mission for Buildings

It Can be Done - but not Without Solar

In a speech at Jodrell Bank, Prime Minister Theresa May outlined her government's  Industrial Strategy and set out a range of so-called Grand Challenge Missions .

These missions include:
  • Using Artificial Intelligence in the Diagnosis and Treatment of Chronic Diseases
  • Meeting the needs of an ageing society
  • Reducing Energy Use in Buildings, and
  • Zero Emissions Vehicles
The missions aim to bring together government, businesses and organisations across the to develop 'industries of the future'.

According to the government website, for buildings the mission is to :

At least halve the energy use of new buildings by 2030

Heating and powering buildings accounts for 40% of our total energy usage in the UK. By making our buildings more energy efficient and embracing smart technologies, we can cut household energy bills, reduce demand for energy, and boost economic growth while meeting our targets for carbon reduction.

For homes this will mean halving the total use of energy compared to today’s standards for new build. This will include a building’s use of energy for heating and cooling and appliances, but not transport.

The mission also includes a target to reduce the cost of low energy retrofits of existing stock (for example Energiesprong approaches I've already written about), but in this article I'll be taking a look at what it means for new buildings.

Unpacking What The Buildings Mission Means

There's some key phrases in the above announcement, with far-reaching implications.

1. 'use of energy'

Up until now, the energy performance of new homes for Building Regulations has been assessed in terms of carbon dioxide emissions rather than energy. The argument for this has been persuasive - that there are UK carbon budgets to aim for and policies should be directly targeted towards achieving this.

However, as grid electricity has decarbonised rapidly, it has created a significant challenge for this approach. With very low carbon electricity, it would be possible to meet regulations for low carbon emissions in buildings simply by heating electrically and doing the bare minimum on energy efficiency. Clearly, adding many new buildings of low energy efficiency this would make the task of maintaining a low carbon grid that much more difficult.

Secondly, and increasingly, the time of day that you take off electricity from the grid affects the carbon intensity (and price) of your energy. Smart technologies are available that control energy use that has flexibility in its timing (technologies such as heating, running a washing machine, cycling a fridge freezer, charging an electric vehicle or discharging a domestic battery). Though consumers are likely to favour technologies that lower their energy costs, periods of low wholesale energy prices tend to coincide with periods of low demand and therefore a high proportion of renewable energy input.  So these technologies will reduce carbon emissions and bills. 

Regulations will struggle to keep up with the complexity and innovation as this sector develops. Using an average grid carbon intensity will fail to incentivise or account for these valuable approaches.

As an 'energy consuming product' it makes far more sense for regulations for buildings to move to energy consumption rather than carbon emissions . Of course, the lower the energy consumption, the less energy is needed and the easier it will be to lower carbon emissions in the electricity supply.
Yet to be determined is what measure of energy we're talking about. If it is straightforward energy use, then one kilowatt hour (kWh) of gas burned to heat the house will count the same as a kWh of electricity taken from the grid. If, instead, it is Primary Energy (which takes into account conversion efficiencies from the original fuel), then electricity use will count more highly than gas.

2.'compared to today's standards'

Progress on carbon emissions is often measured against 1990 levels - the base year for Annex I parties to the Kyoto Protocol, the countries that signed up in 1997. The UK Zero Carbon Homes policy was enacted in 2007, and progress on energy efficiency standards for buildings has been measured relative to a building constructed to 2006 building regulations.

Improvements in energy efficiency of new build homes has been less than impressive. In the 12 years since 2006, the regulated carbon emissions from a new home built in England is only 29% lower than a house built in 2006. Scotland has pushed further forward, homes built here achieve carbon emissions levels 45% better than 2006.

Significantly, the comparison will be relative to today's performance levels. Progress to date will not count towards the mission.

3. 'include a building's use of energy for heating and cooling and appliances'

Until now, Building Regulations have only including 'regulated' energy - that used for heating, hot water, pumps fans and fixed lighting. In homes the regulations ignore energy used for cooking, fridges, freezers, washing machines, dishwashers, clothes dryers, audio visual equipment, IT equipment, plug in lighting and charging battery powered devices.

Housebuilders argue that they shouldn’t be held responsible for the electrical equipment that people use in the homes they build, and the government has up until now accepted that argument.

But why stop there?  Surely housebuilders cannot be held responsible for how often people choose to take a shower, or the fact that they don't want to wear thermals and down jackets while they're watching TV. The precedent of taking an average for domestic hot water use and internal temperature is well accepted, so there's no reason why we shouldn’t regulate based on an average electricity use for appliances and gadgets too.

Still to be clarified is how appliances will be defined – what will be included in electricity use. SAP includes Appendix L with a methodology to calculate the energy use for lighting and electrical appliances and cooking, but it is not clear what range of electrical equipment is included in this estimate and what is not, or indeed whether this estimate of energy for appliances will be used for the Mission

Achieving the Mission

The Solar Trade Association has commissioned analysis by Think Three Consultancy on the future direction for building regulations in a world of low-carbon electricity. The report used SAP 9.92 with new SAP 10 carbon emissions factors to model the energy use a number of house types with a variety of combinations of heating technologies and fabric performance. The 3-bedroom, 94m2 end terrace house modelled in the report, has been used to assess potential approaches towards reducing energy by 50% from today’s performance.

For a home like this built to current regulations in England, space heating and hot water are the dominant energy uses. However, the total of regulated and unregulated electricity use for appliances, lighting, pumps and fans represents 41% of energy use.

Increasing the fabric specification of the building significantly (to Passivhaus levels) greatly reduces the demand for space heating, but leaves all the other energy demands unaffected. A solar PV system of 3.9kWp (12 panels based on high performance panels available today) would be easily accommodated on a house of this size and would bridge the gap from this specification to the mission target.

Improved fabric in combination with a heat pump reduces the space heating and hot water energy by the coefficient of performance of the heat pump (assumed to be 2.5 for heating and 2.0 for hot water). A solar PV system of only 1.2kWp (around 4 panels) would enable this design to meet the Mission target.  

Clearly designers will look for the most cost effective combinations, which as the cost of solar energy declines could involve more solar than this analysis suggests, but given the inclusion of appliance energy use, there seems to be no way to get to 50% reduction that doesn't need solar electricity generation on the building.


1. The Mission can be achieved without the development of fundamental new technological approaches.  Single self-build homes and small developments of social housing are routinely being built to Passivhaus levels of fabric efficiency today. Heat pumps and solar PV are available today. The challenge is more around helping the construction industry deliver high specification fabric efficiencies at volume.

2. The inclusion of energy use by appliances means that the target simply cannot be achieved without some element of renewable electricity generation on the building.

3. The requirement for on-site renewable generation will be even more the case for buildings with form factors that give lower heat losses such as terrace homes and apartments – here there are less gains to be made by improved building fabric and more efficient heating systems.

4. Gas heating currently has Primary Energy Factor (PEF) of 1.222 whereas electricity has PEF 1.738 (SAP10 figures). Unless the PEF for grid electricity falls over the period, a move to electric heating technologies from gas heating will have smaller benefits if the metric is Primary Energy. The more renewable generation on buildings, the more contributions these can make to reducing the PEF of grid electricity.

5. In recognition of the above, forthcoming updates to building regulations should be framed in a way that encourages the use of solar PV on new buildings. 

Thursday, 23 August 2018

SAP 10 - Big Changes Afoot for Solar

Image: Viridian Solar

A new version of the Government's Standard Assessment Procedure (SAP) for the calculation of energy use in dwellings has been published and it contains a number of changes to the way the impact of solar technologies is assessed. 

The key outputs of the calculation described in SAP are:

Dwelling Emission Rate (DER) - the carbon emissions from energy use to heat the house, provide hot water and power lighting, pumps and ventilation. It is expressed in kgCO2 per square metre of floor area per year.

SAP Score - a figure rating the energy costs normalised by floor area to heat the house , provide hot water and power lighting, pumps and ventilation. A house with a score of 100 has energy cost of zero each year, a house with a score of 0 has huge energy costs. The scores from 0-100 are divided into bands corresponding to EPC ratings from 'A' to 'G'

Fabric Energy Efficiency (FEE) - the space heating requirements for the dwelling in kWh/m2

Energy Consumption per Unit Floor Area - which can exclude plug-in appliances (as the above measures do), or include an allowance for appliances and electrical equipment.

Not Just for New Build

SAP is used to calculate the energy efficiency of newly built homes to meet Building Regulations. New homes must currently have a Fabric Energy Efficiency and Dwelling Emission Rate below a mandatory maximum.

Through Reduced Dataset SAP (or RdSAP), the calculation is also used to generate Energy Performance Certificates for existing properties. Over time the SAP rating of homes has become embedded in a range of government initiatives and incentives, for example EESSH in Scotland requires that all social rented homes in Scotland achieve a minimum SAP score by a certain date, and access to preferential Feed in Tariffs are linked to the house having an EPC rating higher than D.

What's Changed?

Carbon Intensity of Grid Electricity

The electricity grid has decarbonised with the move away from coal burning power stations and greater input from gas fired generation and from renewables (see my blog on this subject here). The proposal is to reduce the carbon intensity of electricity from 0.519kgCO2/kWh in SAP 2012 to 0.233 kgCO2/kWh in SAP10.


This is a huge (55%) reduction compared to the current version of SAP, and lower than the figure consulted upon (0.398 gCO2/kWh). However, it is only a reflection of the huge progress that has been made in decarbonising the grid.

The impact for solar photovoltaics is that solar systems will need to be more than double the size of current systems to produce the same carbon benefit in the calculation, which could reduce the competitiveness of solar PV as a means of meeting building regulations. SAP10 will only be brought into use for the next update to the Building Regulations, and government will need to carefully consider whether it is now time to change the primary focus of the regulations away from emissions and towards energy consumption (like for appliances).

For example, emissions from mains gas will be 0.210kgCO2/kWh in SAP10. When you take into account efficiency losses from burning gas in a boiler to heat a house, developers will be able to achieve the same dwelling emissions rate using simple electric heating instead of gas - for example panel heaters and a hot water tank with immersion heater. It may be possible to remove the whole wet heating system and gas supply from new homes, yielding considerable construction and maintenance savings, but possibly saddling house buyers with unaffordable energy bills (unless, perhaps, solar is also fitted).

Export of Solar Generated Electricity

The value of exported electricity in SAP10 is 3.8p/kWh, whereas the cost of grid electricity is 16.6p/kWh on standard tariff. In SAP2012, exported solar electricity is assumed to be of the same value as electricity bought by the householder (which was dubiously justified by the existence of Feed in Tariffs - despite that in solar schemes for social tenants the tariffs went to financiers).

SAP2012 also assumed that 50% of generated electricity was used in the house (called the beta-factor) and 50% exported.  While this generally accepted assumption has started to look rather shaky as installed solar systems got larger, it didn't really matter because the value of exported electricity was the same as the saving made for energy not bought from the grid.

For SAP10, a more sophisticated treatment of the beta factor is used. The proportion of energy used in the house is now a function of the size of the solar system's energy output as a proportion of the energy demand. Larger solar systems attached to small energy demands will have a smaller beta factor and smaller solar systems attched to a large energy demand will have a higher beta factor. Adding a battery into the property will increase the beta factor.

PV diverters can also contribute towards energy for hot water in SAP10, so long as a battery is not present and the hot water cylinder has a sufficient volume (more than daily demand). 80% of generation, less the beta factor is available for input to the hot water cylinder, and the benefit is further diminished by a factor of 0.9 to take into account increased cylinder losses due to higher average storage temperatures.


None of these changes affect the Dwelling Emissions Rate used for current building regulations. Solar PV saves carbon whether the electricity is used in the house or not.

These changes do, however, impact the SAP score and EPC band, as they impact on the calculation of the energy bills associated with the house.

The calculation of the beta factor was derived from a relatively small data-set, some of which was provided to BRE by the Solar Trade Association. An industry group is working to develop a much more comprehensive set of data to improve confidence in the value that SAP produces and to feed into the Microgeneration Certification Scheme guidance to solar / battery installers.


The PV shading penalty has been increased, that for solar thermal remains unchanged.

SAP2012 applies the following penalties to energy production - Modest shade 0.8, Significant shade 0.65, Heavy shade 0.5

SAP10 modifies as follows - Modest shade 0.5, Significant shade 0.35, Heavy shade 0.2
As an alternative the MCS overshading figure can be used.


Industry were concerned about a complex two-step shading calculation process that was proposed in the consultation, and it seems that these concerns were noted, albeit with what look like penalty default values for systems with shading.

Hot Water Demand

A new, more complex calculation for domestic hot water demand reflects the growing importance of this area of energy consumption as increased insulation levels drive down space heating requirements. This is an area that the solar industry has been lobbying for change.

The new calculation takes into account the higher flow rates and lower inlet temperatures associated with the now more common mains hot water showers (either from pressurised hot water cylinders or combi boilers), when compared with header-tank fed systems.

Inlet temperatures have also been reduced for both header tank and mains fed systems as a result of input from the solar industry (by 2-3 degrees).


I calculated a 10% increase in hot water demand for mains pressure fed systems compared to SAP2012. The decrease in inlet temperature will add a further 5% or so to the energy required to heat the water.

An increase in the assumed hot water energy will be welcomed by the solar thermal industry in particular, but higher general energy consumption will aid all energy producing technologies.

Solar Thermal Space Heating

In previous versions of SAP, solar thermal could only be applied to meeting hot water demand, which created an restriction on its potential contribution to household energy demands.

The Solar Trade Association proposed EN 15316-4-3 as a potential route to the inclusion of solar space heating in addition to solar water heating, and provided BRE with guidance and assistance in assessing the new method.

The published version of SAP 10 did not include details of the new method as testing was not complete at the time of publication, so the solar thermal appendix currently has holding text. I will be able to discuss more about how the new calculation works and the results it gives once the final version is revealed.


The solar industry will welcome that SAP includes solar space heating. Less for the opportunities it brings in new build (where space heating demands are limited due to high levels of insulation), rather for the possibilities it opens up to improve the EPC ratings of existing properties with high space heating demand. The domestic Renewable Heat Incentive only supports solar water heating at present due to there being no approved method of 'deeming' (calculating) the expectd savings. The new SAP methodology will open up the enticing prospect of solar themal payments under dRHI linked to heat generated for both water and space heating.

Wednesday, 25 July 2018

Solar By Others

How to Get What you Want and not Get What You're Given

Architects, developers and planning officers often go to exacting lengths to make absolutely sure that they get the look that they're aiming for in a building. For houses that can mean specifying the type of brick, the tile on the roof, and specific styles of windows and doors. Even soffits and guttering do not escape careful scrutiny, selection and specification.

Damn right, too! These materials have a huge impact on the overall appearance of the house and should be defined carefully to preserve the integrity of the design, and the quality and sale-ability of the finished product.

Which makes it all the more surprising to find in developers' design packages a great big rectangle drawn on the roof labelled "solar by others" or "solar by specialist installer".

Surely you know that once you hand over your beautiful, carefully considered design to a Quantity Surveyor, if your specification does not nail down the materials you're looking for, then the words "solar by others" might as well say: "solar - the cheapest you can find, no I honestly don't care what it looks like - yes, I know I was really fussy about the exact make and model of cavity closer, but really, just get what you want for the solar - it's not like anyone will notice it's there."

It doesn't all look this good.  Image credit: ARPower

Solar PV is becoming more and more common on roofs. Incentivised by Feed in Tariffs, more than 800,000 households have now chosen to install solar as a retrofit. Building regulations in Scotland have made solar the norm on new homes and planning conditions in many local authorities (including zero carbon homes in London) also mean new homes are more likely than ever to need solar.

With the coming shift towards electric transport - (the speed of which I predict will take policy makers and energy companies completely by surprise), economies of scale for battery manufacture will drive the availability of cost effective electricity storage, and make solar an even more compelling feature of a mainstream home.

What you Need to Know

The cheapest panels have silver frames, a white backing sheet and polycrystalline cells. Sticking them on a framing system above the roof covering is still (only a little) cheaper than going inline with the roof. If you don't specify what solar you want, this is what you're likely to get.

Here are the choices you face, starting with those that have the greatest impact on 'kerb appeal'.

1. Panel Layout

The number one impact on the overall look of the building is the layout of panels on the roof.  Early design engagement with solar specialists means that cluttered designs fitted around other roofing features can be avoided.  Higher power panels can be selected to achieve energy goals in the most aesthetically balanced way.  See also this guidance on panel design by the  Campaign to Protect Rural England.

2. Frame colour. 

Solar panel frames are most commonly either silver or black. Both have a protective anodised surface finish, but a silver (natural) colour avoids the dyeing process needed to make a black frame so is slightly cheaper.  In most (but not all) situations black frames are considered the most discreet and harmonious choice.

3. Mounting System

Panels can be mounted on metal racking above the tiles or slates or conventional roof covering, or they can be sunk into the roof covering (roof integrated), replacing the conventional roof covering and looking more like an intended part of the building design and less like a 'bolt-on'. Many systems use a 'top clamp' arrangement to hold down the panels to the framing, but some systems have hidden fixings, resulting in a less cluttered finish above the plane of the panels.

Roof integrated systems with visible clamps (top) and invisible fixings (bottom) 

4. Backsheet.

A white backing sheet means you can use ever-so-slightly lower power cells in your panel for the same overall panel output (the white sheet reflects light and keeps temperatures a little lower so the same cells perform better). When combined with mono crystalline cells (which are not quite square and have missing corners), a white backing sheet will produce a characteristic pattern of diamonds running up the panel in columns.

Monocrystalline cells (left) and polycrystalline cells (right) in combination with a white backsheet showing the characteristic diamond pattern of a monocrystalline panel

5. Cell Type. 

Polycrystalline cells are sometimes a similar price to mono crystalline cells, but in times of over-supply often seem to fall further and faster. Right now modules based on polycrystalline cells are around 10% lower in cost than those based on mono crystalline cells. In general poly cells will look a bit bluer than mono, and may have little more colour variation across and between panels , but modern cell production technologies can mean that nowadays they rarely show the crystalline pattern that used to be so characteristic of this type of panel.

(More information on the differences between polycrystalline and monocrystalline cells can be found in this blog).

6. Cell Interconnections. 

Some manufacturers hide the bus-bars (silver strips at the top and bottom edges of the panel that electrically connect the cells together, but obviously this also adds cost. Some panels have cells with rear face connections so there's no silver lines visible on the top face of the panel.

How About Just Asking For Roof Integrated Solar?

For sure there are some great looking roof integrated solar systems available. But specifying roof integrated can still result in a wide range of outcomes when you hand it over to the commercial team. This is particularly the case for roof integration systems that give freedom to use any old panel. 

I took the pictures below at the same site and they show two phases of the same development.  The specification called only for "in-roof solar", opening the door to the silver-framed installations in the lower image which meet the letter, if perhaps not the spirit, of the specification. 

Both are roof integrated solar

For something that has such a big impact on the way a building looks, surely it's time for designers to take control of the solar they get, rather than giving the commercial team carte-blanche to go with the cheapest option offered.  

Unfortunately there’s no substitute for carefully choosing and specifying the product you want, just like you do for other building materials.

Tuesday, 8 May 2018


What is BIPV and what are the advantages of this approach to using solar on our buildings?

Building Integrated Photovoltaics (BIPV) are photovoltaic materials that are used to replace conventional materials to form part of a building envelope.  Buildings come in all sorts of shapes and sizes from the smallest homes to huge tower blocks, but photovoltaics is such a versatile technology that as we'll see the potential applications for BIPV are very wide.


The most obvious location to put BIPV is the places that get the most sunshine.  This is normally high up the building (to avoid shade) and (in the northern hemisphere) tilted towards the south.  Roofing, roof windows and sloping patent glazing are ideal parts of building envelopes where photovoltaic materials can be used.

As part of a refurbishment of Kings Cross railway station, London, the historic barrel-vaulted roofing was renewed in 2014.  The patent glazing at the top of each arch was fitted with 1,400 glass-glass BIPV laminates by Sundog Energy (now part of Photon Energy).  In glass-glass laminates the silicon solar cells are encapsulated in clear plastic and sandwiched between two clear sheets of glass.  The gaps between cells allow light transmission into the building through the BIPV laminates.  Both sides of the apex were treated in this way, facing east and west.

Kings Cross Station 
240kWp BIPV patent glazing, generating 175,000kWh/year ( 730kWh/kWp)

At the Ziekenhuis (hospital) in Aalst, Belgium, an eye-shaped atrium is formed from sloping curtain walling system with glass-glass BIPV laminates supplied by SAPA building systems forming the entire cladding.  Cells are spaced further apart than in a standard PV panel to create the desired light transmission into the atrium behind, resulting in a beautiful dappled light in the enclosed space.

Ziekenhuis, Aalst, Belgium 
46kWp sloping curtain walling, generating 31,000kWh/year (675 kWh/kWp)

It's not only new build projects that can benefit from BIPV.  The renovation of the Appleton Tower at Edinburgh University included 80 solar PV modules attached to the building with the Schletter Efa facade mounting system by installers Absolute Solar and Wind.

Appleton Tower, Edinburgh University
26kWp facade cladding, generating 19,000kWh/year (703 kWh/kWp)

At a more modest scale, buildings such as homes and offices often have a sloping roof covered with tiles or slate.  Here, more standardised BIPV products are available that replace the tiles and slates.

This house in Cambridgeshire has a patch of BIPV solar interlocking tiles, each tile replacing a row of standard concrete tiles.

Tile format BIPV integrated in concrete interlocking tiles

This roof is on the set of "Desperate Housewives" where Elon Musk launched his BIPV glass slates and tiles.  Details of these products are still emerging as (aside from those of Tesla executives), only one or two homes have been completed with this product.  Early indications are that this is a premium product with a very high price - one of the first customers said the product was "not for financially sensitive people", describing an installation process that took 10-15 people 2 weeks and cost him $100,000.

Tesla glass slates for launch event, Desperate Housewives set, California

A more cost effective approach is to take advantage of the huge economies of scale in solar PV panels that are mass produced in standard formats and figure out a clever way to make them part of the roof covering.  This house near York has Clearline fusion roof integrated solar panels covering the whole roof.  The installer, The Phoenix Works were involved in the design of the new build eco home from an early stage so could work closely with the architect, with stunning results.

Whole roof BIPV roof on a new eco home
6kWp Clearline Fusion roof integrated solar from Viridian Solar

Walls and Facades

Of course as building become taller, the available roof area becomes ever smaller in proportion to the building size.  However, an unshaded south facing vertical wall will still get 70% as much incident light each year as an unshaded south facing pitched roof at optimum angle, and a much larger available surface area on the walls can easily makes up for any shortfall

The very first large scale BIPV project in the UK was a facade system on the Northumberland Building at the University of Northumbria in Newcastle upon Tyne.  BIPV solar was installed to a south facing wall as part of a building renovation in 1994.   The 85Wp BP Solar modules were mounted on frames on a south facing facade, tilted to catch more light and to partially shade the windows below from the high summer sun, so helping the building avoid over-heating in summer.

Northumberland Building, University of Northumbria, Newcastle upon Tyne
40kWp facade and solar shade, generating 25,000kWh/year (625 kWp/kWh)

Fast forward to the present day and the 230m high Heron Tower in London, completed in 2011 has 153kWp of glass-glass laminates built into the south elevation of curtain walling in two great stripes running from street level to the top of the tower in front of the two lift shafts.

Heron Tower, London
153kWp BIPV curtain walling  generating 92,000kWh/year (620kWh/kWp)

As well as being a stunning example of what is possible with BIPV, Heron Tower is, unfortunately something of a cautionary tale too.  For across the road  from the south facing elevation at [[110]]] Broadgate, another tower that will top out at 181m is rising from the ground.  When complete this tower will obscure the entire south elevation from direct sunlight for large parts of the day (see image).


We've already seen how BIPV curtain walling and patent glazing can be configured to allow light through, but from time to time reports come out of new materials that will enable the creation of BIPV windows that you can see through but which generate electricity too.  It's normally accompanied by a picture of a hand holding a clear piece of glass.  Sometimes the hand has a latex glove on it.  Most of these remain lab curiosities for the present, however thin film solar panels are already available that are partially transparent.  They tend to finish up with a finish that is either orange in colour or smoked.

Bus station at Bournemouth University has two power generating BIPV canopies
20% transparent CdTe thin film modules from Polysolar

Advantages of BIPV

The principal advantage of BIPV is an aesthetic one.  At its best, BIPV alooks like a considered part of the building, rather than a bolt-on.

New home in Sussex with Clearline fusion roof integrated solar replacing slates

BIPV also produces offset costs - the cost of the materials that you would have used if the BIPV was not there plus the cost of fitting it. Sometimes these costs can be substantial, for example in this project where Welsh slate was substituted for integrated solar PV and the saved costs for slate were equivalent to the cost of the PV roofing.

There are also advantages in the ease of ongoing maintenance compared to bolt-on PV. For example access to tiles on roofs. If a tile fails and needs replacement, the task of doing so is made very much more complex and costly if it is behind an above-roof solar PV system. The system must be decommissioned, removed and the tile replaced before the system is reassembled and recommissioned. A job that could have been completed from a ladder now involves scaffolding and electrical works.

It is becoming evident that birds nesting behind bolt-on solar is an issue, especially for domestic installations where the noise nuisance is disturbing. A mini-industry has sprung up to bird proof above-roof solar by fitting wire mesh around the system.


When you take the time to include solar as part of your design for a new building or refurbishment, BIPV means that your solar can be beautiful as well as functional.